Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the transparency burden. It usefully discloses that the tool performs no WHOIS or ownership lookup, implying a pure lexical operation. It does not mention how irrelevant input fields are handled or what the returned labels look like, but the stated exclusion covers the main risk.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One focused sentence with no filler: the verb and object are front-loaded, and the exclusion ('without WHOIS or ownership data') adds meaningful scope in few words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool is simple and schema coverage is complete, but with nine optional parameters and no output schema, the description leaves room for ambiguity about which parameter to populate and what exact return structure to expect. It is workable but not fully self-sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3; the schema already documents all nine optional string parameters. The description only implies the relevant field is 'host' via 'hostname' and adds no parameter-specific detail beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific operation (split), a specific resource (hostname), and a concrete outcome (labels), and explicitly excludes WHOIS/ownership data. This distinguishes domain-shape from sibling shape/URL tools such as github-repo-shape or normalize-url.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'without WHOIS or ownership data' gives a clear negative boundary: use it for syntactic hostname parsing, not ownership lookup. However, it does not name sibling alternatives or provide explicit when-to-use/when-not-to-use conditions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.